The present invention belongs to the technical fields relating to waveform generating circuits generating voltage waveforms, inkjet head driving circuits driving actuators for ink ejection provided on an inkjet head, and inkjet recording devices provided with an inkjet head having actuators that are driven by such an inkjet head driving circuit.
Conventionally, inkjet heads having actuators for ink ejection are well known, and examples of such actuators of inkjet heads are piezoelectric actuators provided with electrodes on both sides of a piezoelectric element, which constitute a portion of a pressure chamber accommodating the ink. When a pulse-shaped voltage is applied to the electrodes of such an actuator, the actuator is deformed such that the volume of the pressure chamber is reduced, thus creating a pressure in the pressure chamber, which ejects ink drops from a nozzle that is in communication with the pressure chamber.
As shown for example in FIG. 4, the voltage waveform applied to the actuators is made of a first waveform P1 (voltage-falling waveform), at which the potential falls from ground potential to the minimum potential (xe2x88x92Vf), a second waveform P2 continuing the first waveform P1 and maintaining this minimum potential, a third waveform P3 (voltage-rising waveform) continuing the second waveform P2 and rising from the minimum potential to the maximum potential (Vf), a fourth waveform P4 continuing the third waveform P3 and maintaining this maximum potential, and a fifth waveform P5 (voltage falling waveform) continuing the fourth waveform P4 and returning from the maximum potential to ground potential. This series of first to fifth waveforms P1 to P5 constitutes one driving pulse P for ejecting one ink drop from the nozzle, and the driving pulse P is given out repeatedly with a predetermined period.
An example of a waveform generating circuit (inkjet head driving circuit) generating the voltage waveform (driving pulse P) for driving the actuator is shown in FIG. 6. In this drawing, numeral 101 is a CPU, which has two terminals outputting digital signals (for example of 8 bits) for generating the voltage waveform. A first D/A converter 102 for converting a digital signal into a positive analog signal and giving it out and a second D/A converter 103 for converting a digital signal into a negative analog signal and giving it out are connected to the digital signal output terminals of this CPU 101. The first and second D/A converters 102 and 103 receive from the CPU 101 a data set signal together with the digital signals but from a different terminal than the digital signals, and when this data set signal has been input and a predetermined time (data settling time) has elapsed after its input (after the output of the D/A converter 102 (or 103) has settled), the analog voltage is given out. The first D/A converter 102 is connected to a first power source 106 giving out a positive voltage, whereas the second D/A converter 103 is connected to a second power source 107 giving out a negative voltage.
A first and a second voltage/current converter 109 and 110 are respectively connected to the output terminals of the first and the second D/A converter 102 and 103, and these first and second voltage/current converters 109 and 110 convert the positive and the negative analog voltage into currents. The output terminals of the first and second voltage/current converters 109 and 110 are connected to a current/voltage converter amplifier 111, which amplifies the currents into which the voltages have been converted by the first and second voltage/current converters 109 and 110, and converts the amplified currents into a voltage. It should be noted that the first voltage/current converter 109, which is connected to the output terminal of the first D/A converter 102, is connected to the first power source 106, whereas the second voltage/current converter 110, which is connected to the output terminal of the second D/A converter 103, is connected to the second power source 107, and the current/voltage converter amplifier 111 is connected to both the first power source 106 and the second power source 107.
Based on the output voltage from the first and second D/A converters 102 and 103, the first and second voltage/current converters 109 and 110 and the current/voltage converter amplifier 111 generate voltage waveforms like the first to fifth waveforms P1 to P5. More specifically, when the first D/A converter 102 outputs a positive analog voltage and the second D/A converter 103 outputs ground potential, the voltage rising waveform (third waveform P3) is generated, whereas when the second D/A converter 103 outputs a negative analog voltage and the first D/A converter 102 outputs ground potential, the voltage falling waveforms (first and fifth waveforms P1 and P5) are generated. Furthermore, when both D/A converters 102 and 103 output ground potential, waveforms maintaining the potential directly before the output of those ground potentials (second and fourth waveforms P2 and P4) are generated, and the potential between neighboring driving pulses P is maintained at ground potential.
Then, the generated voltage waveform is applied to a multitude of actuators of the inkjet head, through a current amplifier 113, which is made of two transistors 113a, and a driver IC 114. The driver IC 114 includes for example switching transistors that are provided in accordance with the actuators, and, receiving print signals from the CPU 101, selects the actuators corresponding to the nozzles through which ink drops are to be ejected, thus applying the voltage waveform only to the selected actuators.
With a conventional waveform generating circuit as described above, when for example a voltage rising waveform is generated, a digital signal is input into the first D/A converter 102, which outputs a positive analog signal, whereas when the voltage rising waveform is not generated, it is necessary to output a voltage equal to ground potential (depending on the voltage waveform to be generated, there is no limitation to ground potential, and it can be a constant predetermined voltage that is midway between the maximum value and the minimum value of the output voltage of the first D/A converter 102). Furthermore, when the voltage falling waveform is not generated, the output voltage of the second D/A converter 103 needs to be set to ground potential (depending on the voltage waveform to be generated, there is no limitation to ground potential, but can be a constant predetermined voltage that is midway between the maximum value and the minimum value of the output voltage of the second D/A converter 103).
However, due to variations in the characteristics of the D/A converters 102 and 103, it may happen that a voltage that is slightly different from ground potential (or the predetermined voltage) is output, and in the case of such variations in the characteristics, malfunctioning occurs in the current/voltage converter amplifier 111, and a precise voltage waveform cannot be generated anymore.
In view of these facts, it is an object of the present invention to prevent malfunctioning due to variations in the characteristics of the D/A converters with a simple configuration, by improving the configuration of the above-described waveform generating circuit.
In order to attain these objects, the present invention is provided with a switching means whose input can be switched between the output voltage of a D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to a waveform generating portion, wherein the input into the switching means is switched as necessary.
More specifically, according to a first invention, a waveform generating circuit includes at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion, wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is input into the D/A converter, the input into the switching means is switched from the predetermined voltage to the output voltage of the D/A converter.
With this configuration, when a voltage rising waveform or a voltage falling waveform is not generated, the input into the switching means is set to a predetermined voltage that is held constant (for example, the output voltage of a constant voltage source or ground potential), and when a voltage rising waveform or a voltage falling waveform is generated, the input into the switching means is switched from this predetermined voltage to the output voltage of the D/A converter. As a result, when neither a voltage rising waveform nor a voltage falling waveform are generated, a predetermined voltage can be output to the waveform generating portion from, for example, a constant voltage source that can output a precise voltage, even if the D/A converter outputs a voltage that is slightly different from the predetermined voltage due to variations in the characteristics of the D/A converter, so that it is possible to prevent, with a simple configuration, malfunctioning of the waveform generating portion due to variations in the characteristics of the D/A converter.
According to a second invention, in the first invention, the switching means is configured such that the input into the switching means is switched from the predetermined voltage to the output voltage of the D/A converter after the output of the D/A converter has settled.
That is to say, the time from the input of the data set signal until the output of the D/A converter is settled fluctuates depending on the output voltage of the D/A converter and variations in its characteristics, so that if there is no switching means, or even if there is the switching means, but the input into the switching means is switched to the output voltage of the D/A converter before the output of the D/A converter has settled, then the result is variations in the generation timing (output timing) of the voltage rising waveform or the voltage falling waveform by the waveform generating portion. However, in this invention, the input into the switching means is switched to the output voltage of the D/A converter only after the output of the D/A converter has settled, so that the voltage rising waveform or voltage falling waveform can be generated and output substantially at the same time as the switching of the input into the switching means. As a result, variations in the waveform generating timing brought about by fluctuations in the output settling time of the D/A converter can be prevented.
According to a third invention, a waveform generating circuit includes at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion, wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is not input into the D/A converter, the input into the switching means is set to the predetermined voltage.
Here, just like in the first invention, when a voltage rising waveform or a voltage falling waveform is not generated, a precise predetermined voltage can be output to the waveform generating portion, so that it is possible to prevent malfunctioning of the waveform generating portion due to variations in the characteristics of the D/A converter.
According to a fourth invention, a waveform generating circuit includes a first D/A converter that converts a digital signal into a positive analog voltage and outputs the analog voltage, a second D/A converter that converts a digital signal into a negative analog voltage and outputs the analog voltage, a first switching means, whose input can be switched between the output voltage of the first D/A converter and ground potential, and which outputs either that output voltage or ground potential, a second switching means, whose input can be switched between the output voltage of the second D/A converter and ground potential, and which outputs either that output voltage or ground potential, and a waveform generating portion, which generates a voltage rising waveform when the first switching means outputs the output voltage of the first D/A converter and the second switching means outputs ground potential, and which generates a voltage falling waveform when the first switching means outputs ground potential and the second switching means outputs the output voltage of the second D/A converter, wherein the first switching means is configured such that when the digital signal for generating a voltage rising waveform with the waveform generating portion is input into the first D/A converter, then the input into the first switching means is switched from ground potential to the output voltage of the first D/A converter, and wherein the second switching means is configured such that when the digital signal for generating a voltage falling waveform with the waveform generating portion is input into the second D/A converter, then the input into the second switching means is switched from ground potential to the output voltage of the second D/A converter.
Thus, when the voltage rising waveform is not generated, ground potential can be output precisely to the waveform generating portion with the first switching means, even when the output voltage of the first D/A converter cannot be set precisely to ground potential. Moreover, when the voltage falling waveform is not generated, ground potential can be output precisely to the waveform generating portion with the second switching means, even when the output voltage of the second D/A converter cannot be set precisely to ground potential. Consequently, as in the first invention, malfunctioning of the waveform generating portion due to variations in the characteristics of the D/A converters can be prevented.
According to a fifth invention, in the fourth invention, the first switching means is configured such that the input into the first switching means is switched from ground potential to the output voltage of the first D/A converter after the output of the first D/A converter has settled, and wherein the second switching means is configured such that the input into the second switching means is switched from ground potential to the output voltage of the second D/A converter after the output of the second D/A converter has settled.
Thus, the same operational effect as in the second invention can be attained.
A sixth invention is an inkjet head driving circuit driving an actuator for ink ejection provided on an inkjet head, the invention including at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and outputs it to the actuator, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion, wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is input into the D/A converter, the input into the switching means is switched from the predetermined voltage to the output voltage of the D/A converter.
With this invention, the same operational effect as in the first invention can be attained.
According to a seventh invention, in the sixth invention, the switching means is configured such that the input into the switching means is switched from the predetermined voltage to the output voltage of the D/A converter after the output of the D/A converter has settled.
Thus, the same operational effect as in the second invention can be attained.
An eighth invention relates to an inkjet head driving circuit driving an actuator for ink ejection provided on an inkjet head, and includes at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and outputs it to the actuator, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion, wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is not input into the D/A converter, the input into the switching means is set to the predetermined voltage.
Thus, the same operational effect as in the third invention can be attained.
A ninth invention relates to an inkjet head driving circuit driving an actuator for ink ejection provided on an inkjet head, and includes a first D/A converter that converts a digital signal into a positive analog voltage and outputs the analog voltage, a second D/A converter that converts a digital signal into a negative analog voltage and outputs the analog voltage, a first switching means, whose input can be switched between the output voltage of the first D/A converter and ground potential, and which outputs either that output voltage or ground potential, a second switching means, whose input can be switched between the output voltage of the second D/A converter and ground potential, and which outputs either that output voltage or ground potential, and a waveform generating portion, which generates a voltage rising waveform and outputs it to the actuator when the first switching means outputs the output voltage of the first D/A converter and the second switching means outputs ground potential, and which generates a voltage falling waveform when the first switching means outputs ground potential and the second switching means outputs the output voltage of the second D/A converter, wherein the first switching means is configured such that when the digital signal for generating a voltage rising waveform with the waveform generating portion is input into the first D/A converter, then the input into the first switching means is switched from ground potential to the output voltage of the first D/A converter, and wherein the second switching means is configured such that when the digital signal for generating a voltage falling waveform with the waveform generating portion is input into the second D/A converter, then the input into the second switching means is switched from ground potential to the output voltage of the second D/A converter.
Thus, the same operational effect as in the fourth invention can be attained.
According to a tenth invention, in the ninth invention, the first switching means is configured such that the input into the first switching means is switched from ground potential to the output voltage of the first D/A converter after the output of the first D/A converter has settled, and wherein the second switching means is configured such that the input into the second switching means is switched from ground potential to the output voltage of the second D/A converter after the output of the second D/A converter has settled.
Thus, the same operational effect as in the fifth invention can be attained.
An eleventh invention is an invention of an inkjet recording device, including:
an inkjet head having a pressure chamber filled with ink, a nozzle linked to the pressure chamber, and an actuator that is caused to eject the ink inside the pressure chamber through the nozzle by application of a voltage;
a relative movement means that moves the inkjet head and a recording medium relatively to one another; and
an inkjet head driving circuit driving the actuator of the inkjet head;
wherein the inkjet head driving circuit comprises at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and outputs it to the actuator, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion;
wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is input into the D/A converter, the input into the switching means is switched from the predetermined voltage to the output voltage of the D/A converter; and
wherein recording is performed by ejecting ink from the nozzle of the inkjet head onto the recording medium by outputting to the actuator the voltage waveform generated by the waveform generating portion of the inkjet head driving circuit when the inkjet head is moved in relation to the recording medium by the relative movement means.
With this invention, the same operational effect as in the first invention can be attained, and an inkjet recording device with superior ink ejection performance can be easily attained.
According to a twelfth invention, an inkjet recording device includes:
an inkjet head having a pressure chamber filled with ink, a nozzle linked to the pressure chamber, and an actuator that is caused to eject the ink inside the pressure chamber through the nozzle by application of a voltage;
a relative movement means that moves the inkjet head and a recording medium relatively to one another; and
an inkjet head driving circuit driving the actuator of the inkjet head;
wherein the inkjet head driving circuit comprises at least one D/A converter that converts a digital signal into an analog voltage and outputs the analog voltage, a waveform generating portion into which an output voltage of the D/A converter is input, and which generates at least one of a voltage rising waveform and a voltage falling waveform in response to a value of that output voltage, and outputs it to the actuator, and a switching means, whose input can be switched between the output voltage of the D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to the waveform generating portion;
wherein the switching means is configured such that when the digital signal for generating a voltage rising waveform or a voltage falling waveform with the waveform generating portion is not input into the D/A converter, the input into the switching means is set to the predetermined voltage; and
wherein recording is performed by ejecting ink from the nozzle of the inkjet head onto the recording medium by outputting to the actuator the voltage waveform generated by the waveform generating portion of the inkjet head driving circuit when the inkjet head is moved in relation to the recording medium by the relative movement means.
With this invention, the same operational effect as in the third invention can be attained, and an inkjet recording device with superior ink ejection performance can be easily attained.
According to a thirteenth invention, an inkjet recording device includes:
an inkjet head having a pressure chamber filled with ink, a nozzle linked to the pressure chamber, and an actuator that is caused to eject the ink inside the pressure chamber through the nozzle by application of a voltage;
a relative movement means that moves the inkjet head and a recording medium relatively to one another; and
an inkjet head driving circuit driving the actuator of the inkjet head;
wherein the inkjet head driving circuit comprises:
a first D/A converter that converts a digital signal into a positive analog voltage and outputs the analog voltage;
a second D/A converter that converts a digital signal into a negative analog voltage and outputs the analog voltage;
a first switching means, whose input can be switched between the output voltage of the first D/A converter and ground potential, and which outputs either that output voltage or ground potential;
a second switching means, whose input can be switched between the output voltage of the second D/A converter and ground potential, and which outputs either that output voltage or ground potential; and
a waveform generating portion, which generates a voltage rising waveform and outputs it to the actuator when the first switching means outputs the output voltage of the first D/A converter and the second switching means outputs ground potential, and which generates a voltage falling waveform and outputs it to the actuator when the first switching means outputs ground potential and the second switching means outputs the output voltage of the second D/A converter;
wherein the first switching means is configured such that when the digital signal for generating a voltage rising waveform with the waveform generating portion is input into the first D/A converter, then the input into the first switching means is switched from ground potential to the output voltage of the first D/A converter;
wherein the second switching means is configured such that when the digital signal for generating a voltage falling waveform with the waveform generating portion is input into the second D/A converter, then the input into the second switching means is switched from ground potential to the output voltage of the second D/A converter; and
wherein recording is performed by ejecting ink from the nozzle of the inkjet head onto the recording medium by outputting to the actuator the voltage waveform generated by the waveform generating portion of the inkjet head driving circuit when the inkjet head is moved in relation to the recording medium by the relative movement means.
With this invention, the same operational effect as in the fourth invention can be attained, and the ink ejection performance of the inkjet recording device can be improved with a simple circuit configuration.